1. Field of the Invention
The present invention relates to electrolytic cells containing ion exchange membranes. More particularly, it relates to electrolytic cells suitable for an electrolysis of water or aqueous solutions of acids, bases, alkali metal sulfates, alkali metal carbonates, or alkali metal halides and to a process for electrolysis using the same.
2. Description of the Prior Art
An electroconductive material is referred to as an electrically conductive material. An non-electroconductive material is referred to as an electrically non-conductive material.
As a process for producing an alkali metal hydroxide by an electrolysis of an aqueous solution of an alkali metal chloride, a diaphragm method has been mainly employed instead of the mercury method to prevent pollution.
It has been proposed to use an ion exchange membrane in place of asbestos as a diaphragm to produce an alkali metal hydroxide by electrolyzing an aqueous solution of an alkali metal chloride so as to obtain an alkali metal hydroxide having high purity and high concentration.
On the other hand, it has been proposed to save energy in the world. From the viewpoint, it has been required to minimize a cell voltage in such technology.
It has been proposed to reduce a cell voltage by improvements in the materials, compositions and configurations of the anode and cathode and compositions of an ion exchange membrane including the type of ion exchange group.
It has been proposed to attain an electrolysis by the so called solid polymer electrolyte (SPE) type electrolysis of alkali metal chloride wherein a cation exchange membrane of a fluorinated polymer is bonded with gas-liquid permeable catalytic anode on one surface and a gas-liquid permeable catalytic cathode on the other surface of the membrane (U.S. Pat. Nos. 4,224,121 and 4,210,501 and 4,214,958 and 4,217,401).
This electrolytic method is remarkably advantageous as an electrolysis at a lower cell voltage because an electric resistance caused by an electrolyte and an electric resistance caused by bubbles of hydrogen gas and chlorine gas generated in the electrolysis, can be remarkably decreased which have been considered to be difficult to reduce in the conventional electrolysis.
The anode and the cathode in this electrolytic cell are bonded on the surface of the ion exchange membrane to be embedded partially. The gas and the electrolyte solution are readily permeated so as to easily remove, from the electrode, the gas formed by the electrolysis at the electrode layer conducting with the membrane. Such porous electrode is usually made of a thin porous layer which is formed by uniformly mixing particles which act as an anode or a cathode with a binder, further graphite or the other electric conductive material. However, it has been found that when an electrolytic cell having an ion exchange membrane bonded directly to the electrode is used, the anode in the electrolytic cell is brought into contact with hydroxyl ion which is reversely diffused from the cathode compartment, and accordingly, both of chlorine resistance and an alkaline resistance for anode material are required and an expensive material must be used. When the electrode layer is bonded to the ion exchange membrane, gas is formed by the electrode reaction at the electrode membrane interface and deformation phenomenon of the ion exchange membrane occurs which causes the characterstics of the membrane to deteriorate. As a result it is difficult to maintain the cell stable for long periods. In such electrolytic cell, the current collector for electric supply to the electrode layer bonded to the ion exchange membrane should closely contact with the electrode layer. When a firm contact is not obtained, the cell voltage may be increased. The cell structure for securely contacting the current collector with the electrode layer is disadvantageously complicated.